Piston ring and cylinder liner having minute oil-retaining indentation

ABSTRACT

A piston ring or cylinder liner having on its sliding surface numerous minute indentations in a geometric grid pattern, said indentations being formed by closely spaced continuous helical grooves each formed in said surface with a repetitive depth variation to form thereby closely spaced successive ridges and valleys in each groove and with the spacing between successive of said ridges being less than the groove width.

United States Patent Kumabe et al.

[451 Dec. 25, 1973 PISTON RING AND CYLINDER LINER HAVING MINUTEOIL-RETAINING INDENTATION Inventors: Junichiro Kumabe, Tokyo; KoichiShimuzu, Okaya, both of Japan Assignees: Rikagaku Kenkyusho, Wako-shi,

Saitama-ken; Teikoku Piston Ring Co., Ltd., Tokyo, both of J apan Filed:Nov. 30, 1970 Appl. No.: 93,568

Foreign Application Priority Data Dec. 1, 1969 Japan 44/95716 Dec. 1,1969 Japan 44/95717 US. Cl 277/213, 277/214, 92/169 Int. Cl. Fl6j 9/12,F16j 11/04 Field of Search 123/193; 92/169,

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,133,041 11/1956France 92/169 Primary Examiner-Samuel B. Rothberg Att0rney-William D.Hall, Elliott 1. Pollock, Fred C. Philpitt, George Vande Sande, CharlesF. Steininger and Robert R. Priddy 5 7 1 ABSTRACT 5 Claims, 9 DrawingFigures PAIENTEU use 25 I975 sum 1 BF 2 INVENTOR U .M m H S K E B A M UK d BY WM Z/WL KM ATTORNEY PATENIED DEC 2 5 I975 3381.022 SHEET 2 OF 2 Rm m V m d. KUMA BE 4' K. SHIMIZU /7 M Ma VMJM ATTORNEY PISTON RING ANDCYLINDER LINER HAVING MINUTE OIL-RETAINING INDENTATION SUMMARY OF THEINVENTION Introduction of high performance engines in recent years hasbrought a serious problem of the effects of seizure and irregularabrasion due to scuffing of their cylinders and piston rings upon therunning of the engines. The current tendency is that more and more suchdefects are being detected as a result of increases in the meaneffective pressure, explosion pressure, and engine speed for higheroutputs.

Since scuffing is in many cases attributed to the coarseness of theouter surface of piston rings and the inner surface of cylinders,extensive efforts have been made to solve the problem throughimprovements of the casting and machining of such parts. As yet,however, no fundamental solution has been found out. For this reason, ahigh-speed run immediately after the assembling of an engine isprohibited, and some negative makeshift must be resorted to, as forexample many hours of running-in before full-speed operation.

Hard chrome plated piston rings and cylinder liners, which are typicalof the parts in use, are formed with oil-retaining pores. However, theplating by nature makes it difficult to control the irregularity of suchpores, and again these parts require lengthy running-in periods.

On the other hand, improvements in composition are being achieved fornon-plated piston rings and cylinder liners. Nevertheless, the formationof a workdeteriorated layer cannot be prevented. The layer in the formof irregularly distributed regions has very poor resistance to thesliding abrasion at the time of precision finishing, boring, or honing.Their microscopic surface contours consist of irregular indentationswhich form abnormal extreme-pressure contacting parts. They presentdifficulties for localized retention of oil film and increase thechances of unusual high-pressure contact, thus making for a scuffingtendency. These surface characteristics represent the limitations of theprior art machining techniques, and this is the reason why many hours ofthe inefficient, cumbersome and costly running-in operation has to beresorted to customarily under light load.

This invention relates to a piston ring and a cylinder liner whichovercome all of the foregoing difficulties of the conventional parts.More specifically, the invention relates to a piston ring and a cylinderliner which are formed with numerous oil-retaining indentations in ageometrically uniform and regular grid pattern on the entire outerperipheral surface or the entire inner surface, respectively, to avoidthe forming of abnormal extreme-pressure contacting parts and render itpossible to obtain ideal lubricative-contact surface conditions after ashort running-in period.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a piston ringhaving minute oil-retaining indentations of a geometric grid pattern onthe surface in accordance with the present invention;

FIG. 2 is a front view of the piston ring as seen from thedirection'indicated by an arrow mark I] in FIG. 1;

FIG. 3 is a side view of a cylinder liner having minute oil-retainingindentations of a geometric grid pattern on the surface in accordancewith the invention;

FIG. 4 is a sectional view taken along the line lV-IV of FIG. 3;

FIG. 5 is an enlarged view showing the surface conditions ofa part ofpiston ring tha characterize this invention;

FIG. 6 is an axial sectional view showing a piston ring of the inventionin contact with a conventional cylinder liner;

FIG. 7 is a sectional view of the same parts but as seen from thedirection atright angles to their axial direction;

FIG. 8 is a side view of an arrangement for machining the outerperipheral surface of a piston ring according to the invention; and

FIG. 9 is a side view of an arrangement for machining the inner surfaceof a cylinder liner according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will bebetter understood by the following detailed description taken inconjunction with the accompanying drawings showing embodiments thereof.

FIG. 1 is a side view of a piston ring 1 according to this invention,and FIG. 2 is a front view of the same ring, both showing the outwardappearance of the ring covered with continuous rows of numerous fineoilretaining indentations arranged in a geometric grid pattern. Thegeometric grid pattern is formed of indentations distributed withregular pitches in the circumferential direction of the piston ring 1.FIGS. 3 and 4 show, respectively, one side of a cylinder liner 2according to the invention and a central section along the longitudinaldirection of the same liner, the latter illustrating the surfaceconditions of the cylinder liner formed with indentations by the feedpitch S of the boring tool and with indentations distributed with aregular pitch I in the circumferential direction by regular forcedvibration which is produced by the machine tool dynamic rigidity of thetool edge and the cutting conditions. Conventional piston rings andcylinder liners to not have such circumferentially and regularlydistributed indentations.

FIG. 5 shows a microscopic structure of the surface of the piston ring Iof FIG. 2 or the cylinder liner 2 of FIG. 4. In the figure, axial linesa, b, c, d, e, f, and so forth on the piston ring 1 or the cylinderliner 2 represent ridges which define valleys or notches in between, orbetween the lines a-b, b-c, c-d and so forth. Of circumferential linesA, B, C, D, E, F, G, H and so forth, the alternate lines A, C, E, G andso forth represent ridges whereas the other alternate lines B, D, F, Hand so forth represent the bottoms of valleys or notches. It followsthat the piston ring 1 or the cylinder liner 2, as the case may be,contacts the smooth surface ofa conventional matching element with theprominences or distinct points indicated by solid dots in FIG. 5;

The indentations have fine pitches, for example 1 15 ,u. and S 20 IL.All of the surface indentations other than the prominent contact pointsserve as minute oilretaining units, and the oil trapped thereincontributes to smooth lubrication of the contacting parts. Thus, thesurface has a geometric pattern with a grid or mesh of the minuteoil-retaining notches.

FIG. 6 is an axial section ofa cylinder liner in an engine, and FIG. 7is a section at right angles to the axis of FIG. 6, either figureshowing a piston ring 1 of the invention in contact with a conventionalcylinder liner 2'.

As shown, the outer peripheral surface of the piston ring 1 havingoil-retaining notches 3 slides in contact with the inner surface of thecylinder liner 2. The surface prominences of such a piston ring or sucha cylinder liner combined with a conventional piston ring, having theuniform height and regular shape, can complete the initial abrasionafter a very short period of running-in and, with an even contactingsurface, it can proceed to the stage of normal, constant abrasion. Afterthe running-in, the lubricating effect by the countless oil-retainingnotches regularly distributed over the contacting surface can improvethe wear resistance of the mating parts.

H68. 8 and 9 illustrate examples of apparatus for machining such apiston ring or cylinder liner. A workpiece 4 of piston ring or cylinderliner which is rotatably chucked to the spindle of a lathe is machinedwith a cutting tool 5. The tool 5 is designed for resonance with asingle wave mode of bending vibration, and is fixed with vibrationjoints 6 to a tool rest 7, so that the tool tip can be subjected toregular forced vibrations. To avoid any restriction of the vibrationmode, the tool rest 7 is secured to a tool holder 9 which, in turn, isfixedly mounted on a carriage 8 of the lathe. With such an arrangement,the dynamic characteristic conditions and machining conditions to beused are carefully considered and chosen, and uniform and sustainedvibration of the tool tip is ensured. Then, the peripheral or endcutting or boring is carried out.

EXAMPLE 1 A workpiece for piston ring, measuring 50 mm in outsidediameter, 44 mm in inside diameter and 8 mm in thickness, was machinedunder the conditions of spindle speed 220 r.p.m., overall tool length150 mm, node-to-node distance 88 mm, rake angle 0, depth of cut 0.05 mm,and feed 0.06 mm/rev, and regular indentations of geometric grid patternhaving pitches of I p. and S 60 u were formed.

The time required for running-in of the engine using this piston ringcould be reduced to one-third to onefifth of the running-in periods withconventional piston rings.

EXAMPLE 2 A workpiece 4 for cylinder liner, having inside diameter of400 mm, outside diameter of 440 mm and length of 800 mm, was machinedunder the conditions of spindle speed 25 rpm, tool holder 9 length 500mm, holder diameter mm, tool shank thickness 17 mm, tool shank lengthmm, node-to-node distance 88 mm, rake angle 0, depth of cut 0.05 mm andfeed 0.8 mm. Regular indentations of geometric grid pattern havingpitches of I 16 p. and S 800 p. resulted. The time required for therunning-in of the engine using this cylinder liner was as short as aboutone-third to onefifth of the time required with conventional liners.

As will be clear from FIG. I, the present invention is as advantageouslyapplicable to the end faces and inner surface of a piston ring 1 as onits outer peripheral surface.

What we claim is:

1. A metallic part having a cylindrical surface thereof which is adaptedto be in sliding, pressured, lubricated contact with a mating metallicelement to provide a high-pressure seal therebetween,

said cylindrical surface of said part having a myriad of minuteindentations which are disposed in a regular, geometric grid pattern, v

said indentations being defined by closely spaced continuous helicalgrooves each formed in said surface with a repetitive depth variation toform thereby closely spaced successive ridges and valleys in each grooveand with the spacing between successive of said ridges being less thanthe groove width.

2. The invention as defined in claim 1 wherein said metallic part is apiston ring and said grid pattern is formed on the outer cylindricalsurface of said ring.

3. The invention as defined in claim 2 wherein the width of each helicalgroove is about 60 microns and the circumferential spacing betweensuccessive of said ridges in any groove being about 20 microns.

4. The invention as defined in claim 1 wherein said metallic part is acylinder liner and said grid pattern is formed on the inner cylindricalsurface of said cylinder liner.

5. The invention as defined in claim 4 wherein the width of each helicalgroove is about 800 microns and the circumferential spacing betweensuccessive of said ridges in any groove being about 16 microns.

1. A metallic part having a cylindrical surface thereof which is adapted to be in sliding, pressured, lubricated contact with a mating metallic element to provide a high-pressure seal therebetween, said cylindrical surface of said part having a myriad of minute indentations which are disposed in a regular, geometric grid pattern, said indentations being defined by closely spaced continuous helical grooves each formed in said surface with a repetitive depth variation to form thereby closely spaced successive ridges and valleys in each groove and with the spacing between successive of said ridges being less than the groove width.
 2. The invention as defined in claim 1 wherein said metallic part is a piston ring and said grid pattern is formed on the outer cylindrical surface of said ring.
 3. The invention as defined in claim 2 wherein the width of each helical groove is about 60 microns and the circumferential spacing betwEen successive of said ridges in any groove being about 20 microns.
 4. The invention as defined in claim 1 wherein said metallic part is a cylinder liner and said grid pattern is formed on the inner cylindrical surface of said cylinder liner.
 5. The invention as defined in claim 4 wherein the width of each helical groove is about 800 microns and the circumferential spacing between successive of said ridges in any groove being about 16 microns. 